If you move past an archer NPC (specifically only tested with Guerrillas mind you) whist in invis, and they hear you and start firing (which is fine), they will continue to fire at you even if you run far away (which doesn't make sense).
You still get the 50% concealment bonus, so take it as the archer is taking blind potshots. This is due to their acute listen check. Any monsters that does a listen check will be able to do this except for guerillas this statistic may be higher. Sometimes they let go, sometimes they dont.
This isn't something we can control as when they don't, it's usually the targetting bug.
I've been able to break the AI chasing after me when I'm invisible and had been heard. Usually it involves running around a corner to break line-of-sight (as weird as that may be).
I've been able to break it by recasting Invis.
Hitting Hide/MS button works as well.